1. Field of the Invention
This invention relates to substantially amorphous fluorinated vinyl ether copolymers having low glass transition temperatures.
2. Background
Known elastomeric copolymers of tetrafluoroethylene (TFE) and perfluoromethylvinyl ether (PMVE) are useful because of their high temperature and chemical resistances. These copolymers are usually crosslinked (cured) to a three-dimensional network so that they resist permanent deformation in use. Curesite monomers are incorporated into the TFE/PMVE polymers in low concentrations (1-4%). Although these polymers are useful at very high temperatures, their usefulness at low temperatures is limited by the glass transition temperature, Tg, of the polymer. When the environmental temperature drops below the Tg, the polymer becomes stiff or brittle and non-elastomeric. The Tg of TFE/PMVE polymers is relatively insensitive to polymer composition, varying only from -10.degree. C. to -15.degree. C. when the PMVE content of the polymer ranges from 20 mole % to about 50 mole %. Because of its low concentration, the curesite monomer has practically no effect on Tg; hence, the usefulness of TFE/PMVE polymers is limited to temperatures above about -15.degree. C. One means of obtaining better low temperature properties is to prepare a polymer for example, a polyether, having a more flexible backbone. Polyhexafluoropropylene oxide (poly-HFPO) has a Tg of -50.degree. C. to -60.degree. C. and retains its elastic properties at these temperatures.
Specific publications which provide useful background information for the invention herein are discussed below.
U.S. Pat. No. 3,132,123 discloses perfluoroalkylvinyl ethers of the formula CF.sub.2 .dbd.CF--OR wherein R is perfluoroalkyl. U.S. Pat. No. 3,291,843 discloses a process for preparing fluorinated vinyl ethers which can be represented by the formula CF.sub.2 .dbd.CF(OCF.sub.2 CFR).sub.n OR.sub.f wherein R is F or CF.sub.3, R.sub.f is perfluoroalkyl of 1 to 12 carbon atoms and n is an integer and is 1 to 20. Copolymers of the vinyl ether and tetrafluoroethylene are also disclosed. U.S. Pat. No. 3,322,826 discloses perfluorinated acid fluorides of the formula C.sub.3 F.sub.7 O[CF(CF.sub.3)CF.sub.2 O].sub.n CF(CF.sub.3)COF wherein n is 0 to about 23, prepared by polymerizing HFPO, and that the acid fluorides can be converted to vinyl ethers which can be homopolymerized or copolymerized. U.S. Pat. No. 3,817,960 discloses polymers and tetrafluoroethylene copolymers of perfluorovinyl ethers of the formula CF.sub.3 O(CF.sub.2 O).sub.n CF.sub.2 CF.sub.2 OCF.dbd.CF.sub.2 wherein n is 1 to 5. U.S. Pat. No. 3,450,684 discloses homopolymers and copolymers of fluorocarbon polyethers of the formula XCF.sub.2 CF.sub.2 (OCFXCF.sub.2).sub.n OCF.dbd.CF.sub.2 wherein X is F, Cl or H and n is an integer and is at least 1. U.S. Pat. No. 4,138,426 discloses homopolymers and copolymers of functionally substituted fluorocarbon polyethers of the formula YCF.sub.2 CF.sub.2 O[CF(CF.sub.3)CF.sub.2 O].sub.p CF.dbd.CF.sub.2 wherein Y is COOR, COOH, COOM or CN, p is 1 to 5 and M is alkali metal, ammonium or quaternary ammonium. U.S. Pat. No. 4,330,654 discloses copolymers of functionally substituted fluorinated vinyl ethers which include those of the formula Y(CF.sub.2).sub.a (CFR.sub.f).sub.b (CFR.sub.f).sub.c O[CF(CF.sub.2 X)CF.sub.2 O].sub.n CF.dbd.CF.sub.2 wherein a and b are 0 or an integer greater than 0, c is 0 or 1, the sum of a, b and c is not 0, n is 0 or an integer greater than 0, X is F, Cl or Br and R.sub.f is F, Cl, perfluoroalkyl or chlorofluoroalkyl. A similar disclosure appears in European Patent Application Publication No. 0 041 737. U.S. Pat. No. 4,281,092 discloses elastomeric copolymers of tetrafluoroethylene, a perfluoroalkylvinyl ether and, as a curesite monomer, a functionally substituted fluorovinyl ether of the formula CF.sub.2 .dbd.CF[OCF.sub.2 CF(CF.sub.3)].sub.x O(CF.sub.2).sub.n CN wherein n is 1 to 4 and x is 1 to 2. U.S. Pat. No. 3,467,638 discloses elastomeric curable copolymers of vinyl monomers and monomers of the formula C.sub.6 F.sub. 5 O[CF(CF.sub.3)CF.sub.2 O].sub.n CF.dbd.CF.sub.2 wherein n is 0, 1 or 2.
Kalb et al., Advances in Chemistry Series 129, American Chemical Society, 1973, page 13, disclose elastomeric copolymers of tetrafluoroethylene, perfluoro(methylvinyl ether) (PMVE) and, as a curesite monomer, a vinyl ether of the formula CF.sub.2 .dbd.CFOR.sub.f X wherein R.sub.f is perfluoroalkylene, optionally containing ether oxygen atoms, and X is CN, COOR or OC.sub.6 H.sub.5. The copolymers typically contain about 40% polymerized PMVE and 1-4% of the polymerized curesite monomer. Preparative methods for the polymers include free radical-initiated solution and aqueous emulsion polymerizations, and the use of ammonium persulfate-sodium sulfite redox couple at 40.degree.-100.degree. C. to initiate emulsion polymerization is disclosed.
Hill, J. Macromol. Sci.-Chem., A8(3), 499-529 (1974), discloses the homopolymerization of hexafluoropropylene oxide; the polymers so produced have multiple ether links in the backbone chain and exhibit glass transition temperatures (Tg) as low as -60.degree. C., with retention of flexibility. Also disclosed are reactions of the polymers, having acyl fluoride end groups, to produce chain extended and crosslinked polymers having thermal and chemical resistance.
Barney et al., J. Poly. Sci., A-1, 8, 1091-1098 (1970), disclose the preparation and properties of elastomeric, curable fluorocarbon copolymers of tetrafluoroethylene and perfluoro(methyl vinyl ether), containing 20-50 mole % of the vinyl ether moiety. The glass transition temperatures of the copolymers are -15.degree. C. or higher and are relatively insensitive to the vinyl ether content. Also disclosed is the plasticization of the copolymers with compatible Krytox.RTM. perfluoroalkylpolyether oils prepared from hexafluoropropylene oxide.
U.S. Pat. Nos. 3,310,606; 3,397,191; and 3,326,984 disclose, respectively, divinyl ether monomers of the formulas CF.sub.2 .dbd.CFO(CF.sub.2).sub.n OCF.dbd.CF.sub.2, CF.sub.2 .dbd.CFO(CF.sub.2 CF.sub.2 O).sub.n CF.dbd.CF.sub.2 and CF.sub.2 .dbd.CFO(CF.sub.2).sub.m OCF.dbd.CF.sub.2, and CF.sub.2 .dbd.CFOCF.dbd.CF.sub.2.
European Patent Application Publication No. 0 055 407 discloses fluorine-containing elastomers having low temperature and alcohol resistance, prepared, for example, by free radical emulsion polymerization using redox initiators, and comprised of at least 80 mole percent of polymer repeat units of vinylidene fluoride and a fluorovinyl ether of the formula CF.sub.2 .dbd.CFOX wherein X is C.sub.3 -C.sub.9 perfluoroalkyl having 1 to 3 oxygen atoms; up to 20 mole percent of polymer repeat units of hydrocarbon olefins or other fluoroolefins can be present. Cure sites can be introduced into the elastomers by using appropriate monomers such as perfluoro(2-bromoethylvinyl ether), and the elastomers exhibit glass transition temperatures as low as -38.degree. C. U.S. Pat. No. 4,368,308 is similar in disclosure to the European patent application except that there must be at least 70 mole percent of ethylene and fluorovinyl ether repeat units, X is C.sub.1 -C.sub.9 perfluoroalkyl having at least one oxygen atom, and a glass transition temperature of -46.degree. C. is exemplified.
In general, the art, such as reflected above, suggests that fluorine-containing perhalogenated copolymers having ether links in side chains, rather than in the backbone chain, exhibit glass transition temperatures of about -15.degree. C., below which temperature they lose their flexibility.
It is an object of this invention to provide fluorine-containing perhalogenated copolymers having ether links in the side chains, but not in the backbone chains. Another object is to provide such copolymers which exhibit glass transition temperatures less than -15.degree. C., for example, -100.degree. C. A still further object is to provide such copolymers which are flexible (elastomeric) and which retain their flexibility at temperatures below -15.degree. C., for example, to -100.degree. C. A further object is to provide such copolymers which not only exhibit good low temperature properties, but excellent high temperature properties and chemical inertness as well. Other objects will become apparent hereinafter.